Critical issues emerging from current attempts at inducing transplantation tolerance in the clinic include the need for biomarkers that predict and diagnose tolerance as well as for the identification of barriers to tolerance induction and maintenance. Our preliminary observations have led us to the realization that the durability of the tolerant state is variable and can be unpredictably breached by Listeria infections. The overall goal of the proposed studies Is to determine a mechanistic basis for how Infections can either erode or transiently abrogate robust tolerance after It has been stably established.